The governing body of any county, city, or town may adopt ordinances designating the private roads, within any residential development containing 100 or more lots or residential dwelling units, as highways for law-enforcement purposes. Such ordinance may also provide for certification of road signs and speed limits by private licensed professional engineers using criteria developed by the Commissioner of Highways, and, for law-enforcement purposes, such certification shall have the same effect as if certified by the Commissioner of Highways.
Va. Code § 46.2-1307